1. Field of the Invention
The present invention relates to a variable camshaft phaser for an internal combustion engine.
2. Description of the Prior Art
JP-A 1-134011 discloses a variable camshaft phaser for an internal combustion engine of the type having a camshaft for actuating cylinder valves. According to this known device, the magnitude of relative rotational movement between a cylindrical body of a timing pulley and a stub shaft fixedly secured to a camshaft is determined by the magnitude of axial movement of a slide disposed between the cylindrical body and the stub shaft. The stub shaft is secured to the front end of a camshaft. The slide is integral with a piston disposed in the cylindrical body to define a pressure chamber. A sleeve is slidably disposed within a bore in the stub shaft and biased by a coil spring against the piston so that the piston integral with the slide moves the sleeve against the coil spring in response to supply of oil to the pressure chamber. Slidably disposed in the sleeve is a spool. A motor is fixedly attached to a timing pulley cover and coupled with an actuator pin for the spool to move the spool axially. The spool and sleeve cooperate with each other to form a valve for regulating supply of oil to and discharge thereof from the pressure chamber. The sleeve is formed with an inner circumferential groove and an axial bore communicating with this groove and opening to the pressure chamber. Drilled through the sleeve is a through bore extending from the outer periphery to the inner periphery. This through bore communicates with a passage in the stub shaft to always receive oil from an oil gallery of the engine. The spool has outer circumferential transfer groove. The spool has a closed position in which both supply of oil to and discharge thereof from the pressure chamber are blocked, a supply position in which the transfer groove of the spool establishes fluid communication between the through bore of the sleeve and the inner circumferential groove of the sleeve so that supply of oil to the pressure chamber is allowed, but discharge of oil from the pressure chamber is blocked, and a discharge position in which the inner circumferential groove of the sleeve is drained so that supply of oil to the pressure chamber is blocked and discharge of oil from the pressure chamber is allowed.
An object of the present invention is to provide an alternative to the variable camshaft phaser of the kind mentioned above.